Application help volume: This is the "root" structural element; it contains all the markup for an entire help volume.
all entity declarations . . . <helpvolume> . . . all of your help is included here, either literally or using file entity references . . . <\helpvolume>
If you do not enter this tag, its presence is automatically assumed by the HelpTag software.
All entity declarations must appear before the <helpvolume> start tag.